L ~ .\ . .,. ., , VOLCANIC EVENTS

Possible submarine enmtion, ,,Jriana Islands,,W Pacif-2. A11 times are loca (= GMT + 9 hogrs). A report on this accivity also appears, in the 7 November issue of &IS, . .. i- . '. l . .- , .e ' I An intense .episode. of appgre+nt submarine volcanism was recorded 21-22 September . j by an 11-channel hydrophone aday.on Wake Island, an ocean bottom seismometer off : Japan's Bos0 ,Peninsula, and the:-Polynesian Seismic Network's Pomariorio station, on Rangiroa @toll.., . ,Strong ac.ti.vityJegan at about 1100 and peaked between 1230 and 1520, with"severa1 Ebdred .$ist$nct e+en& detected: before the episode ended abfiptly at about 0755 the..next momixigl.. wing the activity, continuous noise levels in the SOFAR clìa&el remained'ät least 50 dB above normal ambient values, at frequencies of 5-30 Hz. ;. T-Phase arrivals at..:the:3 sites were used to determine a rough location for 2 the activity at 21.9"N, 145.9"E, with a typical potential error of about 100 km. However, the calculated position is displaced.more than 200 'km'E' .. .o"f'-the horthern Marianas volcanic arci. falling-on .the.W.edge of. the trench. , ...+ ...... -

' The nearest known submarine volcanic site is frequently active Farailon de Pajaros (Uracas) at.20;53"N, 144.90O.E. Activity was last reported froq the area on 2 September 1985, when a 3-k~nzone.of'discolored water near the 1969 eruption site (about 30 km S of Farallon de Pajaros) was observed from an aircraft. Between 2 August and 5 September 1985, the Polynesian Seismic Network's Rangiroa station recorded 109 T-Phase events, with characteristics typical of submarine eruptions, originating from the NW Pacific. However, no other seismic stations were known to have recorded the activity and a'precise Location was impossible (see SEAN Bulletins v. 10, nos. 9 and 11).

Information Confacts : Daniel 'Walker, Dept. of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822 USA; Jacques'Talandier, Laboratoire de Géophysique, BP 640, Papeete, Tahiti; Yosihiro Sawada, Seismological and Volcanological Department, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.

... "After our previous report Öf. the April-May 1989 eruption. (see SGBulletin v. 14, no. 4), activity.apparently..declinedin early May to the normal level in the cone complex near Marum (figure'l). The previous report of a possible,extra-caldera flow turned out to be erroneous, with the 1989 lava flows staying strictly confined inside the caldera. However, a pilot indicated that on 25 May a white pl~ewas rising to 6000.m, associated with an ash cloud that rose to 3000 m, showing that the volcano remained active. ,. Excerpts from the SEAN Bulletin are printed in EOS, a publication received weekly by members of the American Geophysical Union (2000 Florida Avenue r;fw, Washington, DC, 20009, phone (202) 462-6900; marketing department, toll-free 800:424-2488). The complete Bulletin is available from AGU in the microfiche edition of EOS, as a micro- fiche supplement, or'as a paper reprint. Single issues of the Bulletin on microfiche (from v. 6, no. 1 through the current issue) cost $1.00. For paper reprints (v. 1, no. 1 through the current issue) order SEAN Bulletin (give date and volume number) through AGU Separates: $3.50 for the first'copy of each issue to those who do not have a deposit account; $2.00 to those who do; additional copies of each issue are $1.00. A complete volume of paper reprints (12 issues; 15 in volume 1) costs the annual

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f.:,¡:# , October '31, 1989

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3 mbnVolcano (continued) il 26-30 I "There was no further report until two of us visited the volcano September, gathering complementary information about the recent eruptions and the present level 1i of activity (Monzier and Douglas, 1989). The 1988 and 1989 lava flows originated from /I an area on the S flank of Marum formed by one crater and two cones, one of which was 1; 1-3 :i already visible during a 1943 photographic suarvey. The flows are basaltic aal m thick, highly vesicular and aphyric in 1988, and slightly vesicular 'and plagioclase '! sub-aphyric in 1989. The lava contours have been mapped; one of the 1989 flows 1: partially covered a 1988 flow, while the other (eastern) one rejoined the 1988 flow in I I the SE sector and extended farther E, but stayed inside' the caldera. Observation of the main craters was limited by*poor weather. The Benbow pit was occupied by a gently bubbling lava lake, evident at night by a red glow visible from Sesivi, on the S coast of Ambrym. Marum was slightly degassing. also I The Mbuelesu pit was occupied by a strongly bubbling lava lake but no large explosions were observed. The crater just S of Mbuelesu was in a fumarolic stage, as were the craters from which the recent flows ori

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I I- Figure l: Geologic features of Ambrym caldera from Eissen et al., 1989.' The 1988 and l Q1 1989.lava flow paths have been modified after Monzier and Douglas, 1989. = Tuvio volcanics (old northern Ambrym volcano), 42 - older flank volcanics, 43 - younger flank volcanics, 'Q4 Tower.peak volcanics, Q5 - undifferentiated recent caldera and flank volcanics, 46 - NE and'EaMarum basaltic flows and related old cones.. The area shown is outlined on the indexymap , (inset) of the .main topographic' features of Ambrym Island. B. - Benbow, M - Markm: (active cones), To = Tower Peak; Tu - .Mt."'.Tuvio (old . volcanic.centers), E- Endu village, O = Otas village, S - Sevisi village; ' Maps modifie$iafter geological ..(New Hebrides Geological Survey, 1976) and pedomorphological (Quantin, 1978) maps, of Ambrp,

SEAN Bulletin; v.'14, no. 10 October: 31, 1989

.- .. ... , '. ... .A 4 \ Amb@ Volcano (continued) _...... \ .. - ...... - ,*I "The series of photographic surveys done periodically between 1943 and 1989 allows us to compare the evolution of the morphology of the craters (figure 2). Benbow, source 'of the major historic eruptions (figure 3), does not show any major morphological changes. In'contrast, the morphology of Marum and adjacent cones changed substantially during this period. In 1943, Marum and its eastern neighbor Mbuelesu were both clogged with detrital material. Note that the small '892' cone, from which the recent flows originated, already existed in 1943. In 1953, Marum resumed its activity (Eissen and Louat, in preparation). On the 1954 photos, one new crater ('1953') underlain by fumaroles had formed across the edges of Marum and Mbuelesu Crate&. TWO smalíer cones were also -sible S of the-1953 crater. 1972 photos we can note: 1) the opening of a gently smoking pit in the center of Marum ... I.. AMBRYM CALDERA

Crater; 2) the enlargement and division of ~ 1953 crater, inactive at this time; 3) the ; formation of. a new active crater S of 1953 crater, at the site of the 2 small cones visible in 1954. In 1986, the central pit of Marum and the W part of the 1972 double crater had merged and.were slightly smoking. The E part of the 1972 double crater had enlarged at Mbuelesu and was strongly active and smoking. The 1989 situation is described above.

"Thus, whereas Benbow has remained almost unchanged morphologically during the last 46 ; 1 years, Marum and its adjacent craters strongly I evolved during the same period, and recent activity seems concentrated in this area, restricted to the caldera. Although testimony is fragmental since 1980, strong activity ( seems to have resumed, the presence of 2 lava

t .lakes indicating that the magma column is . I t presently very high. Ambrym has had at least t 7 eruptions .accompanied by extra-caldera lava '1 .! flows, sometimes with resulting destruction - ,: and. casualties. Part of the population has,: . E ' been .evacuated several times (in 1913-15 ,-'.' i U 1929, :and 1951) on adjacent islands. Careful 2 .study, observation, and eventually monitoring C of this volcano should be encouraged to help to f prevent further destruction due extra- ,. ( caldera lava flow( s) that could reasonably .be n expected within: . ..i. the next .....few years." .-.. . t , . - . . - . a Figure 2:: Morphological evolution. of the main A intra-caldera craters'-of ?':"biym ,from- áéria$; y:-, S' photographic surveys done. in .la43 (US >Air ..; ,-, $ Force) , 1954 (Institut Géographique National)'; P: 4 August 1972 (Royal Air Force), and 22 . 2. September 1986 (Royal Australian Air Force),;., SI and from ground observations 27-28.September' 1989 (Monzier and Douglas,,.1989). Symbols: 1 - volcanic cone with detrital filling (dots) ;-., 2 - lava flow; 3 = plume (white or gray); 4 - . fumaroles. SEAN Bulletin, v. 14, no. 10 October 31, 1989

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2000 1774 1850 1900 1950 Figure 3: Tentative chronology of historical eruptions of Ambrym (Eissen and Louat, in preparation):! -1774 corresponds to Captain James Cook's report of activity. The 1850- 1950 period corresponds to miscellaneous reports, mainly about extra-caldera eruptions, the only ones that are a significant threat to the local population. 1950- 1980 observations were by the New Hebrides Geological Survey, before Vanuatu's independence on-1August 1980. Levels of activity: 1 low level, without precise 2 - details; = high level, with heavy a,shfalls and/or lava lake; 3 - eruption with intra-caldera flow(s); 4 = eruption with lateral extra-caldera flows. References: Eissen, J.P. and Louat, R. (in preparation), Chronology of the Historic Volcanic Activity of the New Hebrides Island Arc from 1774 to 1989. Monzier, M. and Douglas, C., 1989, Rapport de Mission à Ambrym (Vanuatu) du 26 au 30 Septembre 1989; Rapport de Mission Géologie-Géophysique no. 10, Document ORSTOM Nouméa, 30 pp. New Hebrides Geological Survey, 1976, Geology of Pentecost and Ambrym; 1:100,000 Sheet 6.

Quantin, P., 1978, Archipel des Nouvelles Hébrides; Atlas des Sols et de Quelques Donées du Milieu; Cartes Pédologíques (1:50,000-1:100,000), des Formes du Relief, Géologiques et de la Végétation (1:100,000-1:250,000), 18 feuilles et 11 notices; ed. ORSTOM. ._ Information Contacts: J.P. Eissen, M. Lardy, and M. Monzier, Centre ORSTOM, BP . .I A5, Nomea cedex, New Caledonia; C. Douglas and L. Mollard, Mission ORSTOM, BP 76, Port Vila, Vanuatu. -. ,._.. .. i.' , 8 ' Sakura-lima Volcano, Kyushu, Japan (31.58"N, 130.67"E): .,,: I '". Ten explösions were recorded in October (table 1.), raising the 1989 total to 21. The activity caused no damage. Maximum plume height was 2200 m above the crater, on 14 0ctober.c' .The.month's ash.accdationat Kagoshima Local Meteorological ..L . Observatory,'. :, ::I 10 km. west of the .crater,was 111 g/m2, (table 2). . .. 'l.. .*'.:;. .22 27 . Date: 10' ¿lI:*>13 . 14 .I6 .25 total 231 29:1 Number': 1 1 :1..;.[1 1 1' 1 1 ,. .l .. 1 . 10,.,; . ... - , ?,-,2'-;3(:- . .- -. ,.- I_ . '.[.d-.. '. =..,...... '1989. Table 1: Number of recorded explosions per day at Sakura-jima, October,' ' 6 7 10 11 16 18 ,!19.,,21 24 25 27 28 Date: . . 5 . . 14 15 30 total .2-:3. O 8 5 9 26 111 Ash (g/m2):. O .1 O 1 5 1 1. 1 11 4' 8. ... 5'. 24- ..2.4 ., . - . ... - \' ,... Table 2: Daily October ash accumulation at the Kagoshima Local Meteorological ' Observatory, 10 km W of the crater.

SEA" 31, 1989 Bulletin, v. 14, no. 10 October 2282 Institution SEAN-. Scientific Event Alert Network .

VOm.14,=NO. 10, OCTOBER 31, 1989

2 Is.) : 21 hours of.: .d volcanic fl . . seismicity . ::2i~~crat;'e'rs~''~-'ch~ges~s~~Ce..... -.. ,y".:,.; ...... J ...... t ...... !1943. des'c%f.ljed, ...... 2-5 ...... 5 Aso (Japan): More explosions; stronger tremor; new vent ...... 6-7 Canlaon (Philippines): Mild ash ejections to 1200 m ...... 7 Taal (Philippines): Increased seismicity; main crater inflation ...... 7-8 Rabaul (New Britain Is.): Seismicity increases slightly; no new deformation . 8 Ulawun (New Britain Is.): Weak-moderate vapor emission ...... 8 Langila (New Britain Is.): Vulcanian explosion; ash to coast; night glow ... 8 Manam (Bismarck Sea): Intermittent vapor release; decreasing seismicity .... 8 Bagana (Bougainville Is.): Frequent rockfalls; weak explosions; glow ...... 9 White Island (New Zealand): Tephra ejections; possible new vent ...... 9 Kilauea (Hawaii): Lava flows into sea at 3 sites; breakouts from lava tubes 10 Ruiz (Colombia): Seismic energy release declines ...... 11 Galeras (Colombia): Seismic activity remains strong; high SO2 ...... 11-12 Pods (Costa Rica): Continued thermal activity from crater lake; sulfur flows 12-13 Arenal (Costa Rica): Volcanic seismicity and recorded explosions increase .. 14 Mt. St. Helens (Washington): Earthquakes in magma conduit ...... 14-15 Etna (Italy): Details of September-October eruption ...... 16-26 Stromboli (Italy): Frequent incandescent tephra ejection similar to 1988 ... 26-27 Vulcano (Italy): Fumaroles deposit sulfur ...... 27-28 'Atmospheric Effects: New aerosols seen Aug/Sept no longer evident ...... 28 EARTHQUAKES Is. 7 Aleutian (M 6.7) Oct.; Japan (M 5.3) 13 Oct.; California (M 7.1) 6.6) 1 18 Oct.,; China (M 5.3) 18 Oct.; Solomon Is. (M 7.1) 27 Oct.; Japan (M 29 Oct.; Algeria (M 6.0) 29 Oct...... 28-29 .: FIREBALLS Y East Germany (2); Hungary; England; Czechoslovakiaflest Germany; Washington, Washington/Oregon (2), Oregon (2), Aleutian Is., Maine, USA; New Zealand . 29-32

-. :i .- . i .: - Lindsay McClelland, Katherine R0mana.k SCIENTIFIC EVENT ALERT NETWORK National Mus-cum of Natural History Mail Stop129=Washington,D.C. 20560*Telephone{202) 357-151 1=Telex 89599SCINET WSH . ( boto ate preliminary and subject to change: contact the &¡gincd source OC SEA N before using )

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